Communication security has been a priority since the beginning of recorded history. The survival of human cultures has always relied on the use of accurate information transported over distances. The interception of this information, preventing its reception or its misuse, can alter the course of nations. As technology advances, so too does the threat to modern satellite communication. The methods of interfering with or intercepting satellite signals are numerous and need to be better understood.

This image was acquired using the 'Privateer' assembly from a passing NOAA satellite. Notice the detail of the California wildfires taking
place in the lower left-hand portion of the image.

As has been demonstrated by a small team of undergraduate students, the capability to intercept the nation's communication satellite signals is no longer limited to national powers but can be mastered by individuals using off-the-shelf technologies.

Defense against signal interception requires reconsideration of spacecraft design in terms of transmission, propulsion, and encoding technologies. It is imperative that efforts be taken to minimize vulnerability and prevent those with hostile intentions from compromising security.

Introduction: The Necessity of Security in Modern Satellite Communication

The issue of communications security is a universal concept stemming throughout recorded history. In ancient kingdoms and nation-states, scribes were specifically appointed by the ruling power. As compensation, they would typically enjoy a life of comfort and safety, relatively rare commodities in for the era in which they lived.The ruling powers would ensure these attributes for a single reason: scribes were the only members of ancient society with the capability to not only produce, but interpret and relay the only means of true long-range communication - writing.

Although scribes played an arguably prominent role in this era and enjoyed more benefits, efforts would have been moot if not for the component by the traveling messenger. Although this charge would typically require fewer skills and less education that the scribes', the assured delivery or transmission of a document often proved paramount to the affairs and concerns of the state for which they served. In some powers of the world at that time, a messenger would often reap the same benefits afforded to a scribe for earned trust, devotion, and success in missions.

The application of these two roles in a world power pre-dating electronic signal communication or modern transportation beyond a horse-back rider or chariot was often pivotal both to policy decisions of the ruling party and the citizens they served. These messenger communications would be considered urgent to the receiver, given that the before mentioned message would over-ride any diplomatic contact and be considered time-sensitive. Often in fact these messages would include declarations of diplomatic foreign concern such as a tribute payment, a warning of intent, or an outright declaration of war. Other necessities requiring this service and its expense would be in the acquiring and timely distribution of intelligence.

Given the often-sensitive nature of these messages, opposing or otherwise hostile powers would often employ the services of those willing to seek out and acquire these messages by any means possible. This role would often be filled by an individual or individuals of an aggressive nature (often a soldier, spy, or otherwise member of the ruling parties' employ) and charged with the pursuit, interception, acquiring, and submission of any captured documentation. Another method of disrupting this communication process would be the corruption (either through bribe, blackmail, or mortal threat) of the scribe. Once turned, the scribe would often be able to provide important intelligence and skills.

An additional concept arose from this effort, specifically from an individual profiteering perspective: piracy. Individual highwayman would patrol transit routes to capture and kill these messengers and sell the information to the highest bidder. Due to the increasingly hazardous nature of a messenger's task the initial ruling party (employing the messenger) would employ newer means as they were developed to help ensure the safe delivery of these often-critical messages. The tasked messengers would be furnished with fast horses, carriages, light weaponry, and any other means for the individual transporter to attain their sponsors' goal as completely and as safely as possible.

As technology improved among the cooperative and opposing nation-states worldwide, new means of communication transmission were developed. Ocean travel, spurred largely by an inherent human need to explore and expand their holdings, became the most prevalent method of transportation and the long-range transmission of written messages. With any advancement, however, a counter-force by an opposing power always faces it. To counter the first parties' additional training, provisions, and transportation of the messengers hostile forces would similarly equip their interceptors.

Similarly, to counter ocean-going transports, fast warships were developed with the capability and armament necessary to intercept, disable, destroy, and otherwise prevent the successful transmission of an opposing forces' intent. This process has continued through the founding of the New World, the development of electronic communication, two world wars, the Cold War between the United states and the former Soviet Union, and ultimately the modern day.

As such, what does the preceding explanation of largely medieval concepts and methods have to do with modern satellite communication security? As with most development throughout the world, technology will change, but concepts and premises remain the same. Earth orbiting satellite communication systems operate on the same general premise that any other communication structures use. Signals are generated to respond to a certain goal of a consumer; this is a role comparable to a scribe in that it is an isolated device singularly capable of utilizing the data. This apparatus must be considered as the processing devices that occupy both the ground stations utilizing the orbiting satellite and the onboard processing unit controlling the spacecraft itself. The signal transmission itself, either sent from the ground station to the satellite, or satellite to the ground station, represents the role of the messenger. Just as the these parallels exist in the operational perspective of satellite communication, so to does the rising challenge of opposing powers working to use these communications against users.

The Overall Threat

The basis of concern in the interception and misuse of satellite ground link systems lies in the mechanics of its operation. In conventional satellite communication up- and downlinks, the satellite utilizes an antenna that is connected to a receiver unit and a transmitter unit, which typically are separate devices. These devices are in turn connected to the satellites' internal Command and Data Handling system or onboard computer that operates all the other spacecraft mechanisms including the thrusters, attitude orientation detection and control, and any other onboard payloads.

In typical orbital operation, a signal is generated onboard the satellite while in orbit. This signal is a function of its mission and intent; an example would be in a typical communications satellite where a signal is received by the receiver from a transmitting ground-station, fed into the onboard computer, and relayed to the transmitter unit. The transmitter applies the signal to the antenna, which projects the signal towards another receiving ground-station
The concern involved in this process lies in the potential prevention or misuse of the communication. As was true in the medieval era, these messages are often crucial and urgent, especially communications sent over a dedicated link as may corporations and governments employ worldwide. Forces opposing these users have and will continue to use methods of disruption of the communication to gain an advantage in competition with those whom the message is actually intended to serve. The two primary means of this disruption in commerce and policy lies in two primary methodologies: preventative action and misuse.

Preventative Action

Preventative action involves the deliberate hindrances of or action taken to prevent a message from continuing to its intended destination. Typically, these measures are only employed during times of open hostilities and with the intent of eliminating an enemies' resources. One method to accomplish this end is satellite signal jamming. Jamming involves the transmission of a large modulated carrier to the receiving terminal of a target approximating the same frequency of the signal the senders are trying to prevent, effectively flooding the receiver with a noise signal and preventing the interpretation of any target signal. Although this may be combated using sequenced modulations in a transmissions data rate, it is an effective means of preventing any signals from being received from a targeted host.

Another method employed is open offensive action. In order to best-prevent any communications interchange, a hostile force might pursue action to simply destroy either a ground-station or orbiting satellite critical to an operation. Although very few attacks on satellites have taken place in the past, advances in technology worldwide in the fields of rocketry, kinetic munitions, and particle weapons ensure that this concept will become a concern in the very near future and have a widespread effect on the nature of warfare.

Misuse

This concept typically raises greater concern than the previous due to its nature. Because its methods of execution are often passive and undetectable, they may be employed during peacetime as an effective means of gathering intelligence. These methods are considered comparable to 'wire-tapping', allowing the aggressor to gain information on the target and use it to an advantage.

One obvious application of this concept that has been applied since well before the invention of satellite communications is in bribed cooperation of a component of the user, effectively 'bribing the scribe'. This concept is applied to satellite technology in that the encryption codes employed may be broken onboard the spacecraft either by a covert informant or code breaking efforts. The end-result of the successful completion of this effort results in the hostile force gaining control of the spacecraft, its information, and capabilities.

Another method which is far less expensive and tasking that the one previously described is ground-based signal interception. This method relies on a relatively widespread signal transmission from the target spacecraft in orbit. Upon transmission of the signal, usually predictable as a function of position and time, a hostile force would employ a small ground-station or listening post within the range of communication. Although it is completely reliant on the user's employment of the communication, this is an effective and undetectable means of gathering intelligence and advantage against the selected target. This method served as the basis of the following research experiment briefly reviewed in the following section of this document in an attempt to employ a similar mechanism and intercept open-source satellite data.